“One factor that may influence egg production is the moon,” observes Bruce Stallsmith. “Many fish … produce eggs in a cycle tightly linked to phases of the moon. Usually they breed best on a new moon, when nights are dark. Some North American killifish are known to do this, for instance, Fundulus heteroclitus, the mummichog, … only breeds when the new moon causes a spring, or very high, tide in the marsh. The eggs remain attached to salt marsh grasses above the water line for four weeks until the next spring tide, when they hatch and the young fall into the water.”
There is no proof that other, inland killifish are so affected, but lunar influence may provide a possible correlation with cycles of egg production.
— G.C.K.A. Newsletter, November 1998